Amplitude of the surface tension near the critical point

In the vicinity of a critical point, along the coexistence curve for a liquid and its vapor (or for a binary mixture below the consolute point), the surface tension vanishes as σ=σ₀(1-TTc)^μ, whereas the correlation length diverges as ξ=ξ₀^-(1-TTc)^-ν. Widom's scaling law relates μ to ν as μ=(d-1)ν ($d<~4$ is the dimensionality). Consequently, the combination of amplitudes (σ₀kTc)(ξ₀^-)^d-1 is universal; the first two terms of the ε expansion for this quantity are computed in this work.